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Renal excretion of calcium and phosphate in preterm and term infants
Insights
Preterm and term infants show similar phosphate and calcium excretion after the first week of life, despite initial differences. Results suggest relative phosphate deficiency impacting bone mineral formation in infants.
Area of Science:
- Neonatal physiology
- Pediatric nephrology
- Nutritional science
Background:
- Urinary phosphate and calcium excretion are critical for infant bone health.
- Understanding these processes in preterm and term infants is essential for optimal growth.
- Breastfeeding is the primary nutrition source, influencing mineral balance.
Purpose of the Study:
- To compare urinary phosphate and calcium excretion in preterm and term infants.
- To investigate changes in mineral excretion during the first three months of life.
- To assess the relationship between phosphate intake and excretion patterns.
Main Methods:
- Prospective study of breast-fed preterm and term infants.
- Measurement of urinary phosphate and calcium levels.
- Analysis of parathyroid hormone and fractional phosphate excretion.
Main Results:
- Higher urinary phosphate excretion in preterm infants during the first week of life.
- Similar phosphate and calcium excretion in both groups after the first week.
- Low fractional phosphate excretion (1-6%) and initially low calcium excretion.
- Increased calcium excretion and high urinary calcium/creatine ratio in preterm infants after two weeks.
Conclusions:
- Infants may experience relative phosphate deficiency, impacting bone mineralization.
- Adaptive low urinary phosphate excretion is observed.
- Elevated urinary calcium excretion suggests potential challenges in bone mineral accretion.
Abstract:
We studied urinary phosphate and calcium excretion in preterm and term infants during the first 3 months of life. The infants were mainly breast-fed, and the average phosphate intake ranged between 0.5 and 1 mmol/kg/day. During the first week of life urinary phosphate excretion was significantly higher in preterm than in term infants, whereas parathyroid hormone values were the same. After the first week of life urinary phosphate and calcium excretion were the same in preterm and term infants. Fractional excretion of phosphate was low (range 1% to 6%). In both groups calcium excretion was low during the first weeks of life, and increased thereafter to 5 and 3 mmol/1.73 m2/day, respectively. The urinary calcium/creatine ratio generally exceeded 2.0 (mmol/mmol) in preterm infants after the second week of life. These results are compatible with a state of relative phosphate deficiency, resulting in an adaptively low urinary phosphate excretion and an inability to form bone minerals, and therefore relatively high urinary calcium excretion.